(species Peltigera canina), foliose (leafy) lichen usually found in patches 5 to 10 cm (2 to 4 inches) in diameter on heaths, sand dunes, walls, or grassy ground. The dull brown thallus with rounded lobes is soft when moist and papery when dry. Because its reproductive bodies resemble the teeth of a dog, it was used as a treatment for rabies in the European Middle Ages; powdered Peltigera was mixed with black pepper and warm milk.